Polyurethane and its use for producing solvent-free coating substances

ABSTRACT

A reactive polyurethane with a number average molecular weight Mn of 800 to 14,000 daltons, a branching degree of 0.0 to 3.0 Mol/kg and an isocyanate functionality of 2.0 to 6.0. The reactive polyurethane is produced by reacting polyester and/or polyether, which both have at least two functional groups that are reactive with isocyanate and which have a molecular weight of 400 to 2,500 daltons and a branching degree of 0 to 3.5 Mol/kg; with at least one polyol with a molecular weight of 62 to 400 daltons and a functionality of 2 to 4; polyamines and/or alkanolamines; compounds with at least one functional group capable of producing anions and at least one functional group that is reactive with isocyanates; polyisocyanates and/or polyisocyanate adducts; blocking agents for the isocyanate groups and neutralizer. Also, a polyurethane dispersion containing the reactive polyurethanes.

The present invention relates to a novel reactive polyurethane and anovel polyurethane dispersion and to the use thereof for preparingsolvent-free coating materials, especially basecoat and/or clearcoat orsolid-color topcoat materials. The present invention further relates toa novel solvent-free coating material which comprises the novelpolyurethane and the novel polyurethane dispersion. The presentinvention additionally relates to a novel process for producingmulticoat coating systems on primed or unprimed substrates. The presentinvention relates not least to novel single-coat or multicoat coatingsystems, especially automotive OEM finishes, industrial coatings,including coil coatings and container coatings, and furniture coatings,and also to substrates which have these novel coatings.

In the context of the present invention, the term “solvent-free” denotesthat the coating material in question is completely free from organicsolvents or contains only the small amounts of organic solvents normallyintroduced by way of the starting products.

It is a general object to provide, for industrial processing, coatingmaterials which release a minimum of volatile organic substances onprocessing.

Known are:

1. Solvent-free coating materials based on primary polymer dispersions,but which give rise to diffusion-impervious, stable, glossy coatingsonly in combination with dissolved cobinders and cosolvents.

2. Coating materials based on secondary dispersions, especiallypolyacrylate, polyester or polyurethane dispersions, but which againonly give impervious, stable, glossy coatings with fractions ofcosolvents and which, moreover, tend toward popping during applicationand film forming.

3. Solvent-free coating systems in the form of powder coatings or powdercoating slurries, which are able to form impervious, smooth, glossycoatings, but whose preparation requires considerable effort and whoseapplication, especially in the case of powder coating materials,requires special equipment.

It is an object of the present invention to provide a novel solvent-freecoating material which no longer has the disadvantages of the prior artbut instead may be processed and applied by the conventional applicationmethods with substantially no emission of volatile organic substancesand which after curing gives impervious, stable, glossy coatings.

The invention accordingly provides the novel reactive polyurethane (1)having a number-average molecular weight Mn of from 800 to 14000daltons, a degree of branching of from 0.0 to 3.0 mol/kg, and anisocyanate functionality of from 2.0 to 6.0, which is preparable byreacting with one another

(1.1) at least one polyester and/or

(1.2) at least one polyether, both of which have at least twoisocyanate-reactive functional groups, a molecular mass of from 400 to2500 daltons and a degree of branching of from 0 to 3.5 mol/kg;

(1.3) at least one polyol having a molecular mass of from 62 to 400daltons and a functionality of from 2 to 4 and/or

(1.4) at least one polyamine and/or

(1.5) at least one alkanolamine;

(1.6) at least one compound having at least one functional group capableof forming anions and at least one, in particular at least two,isocyanate-reactive functional groups;

(1.7) at least one polyisocyanate and/or

(1.8) at least one polyisocyanate adduct;

(1.9) at least one blocking agent for the isocyanate groups, which areeliminated again at a certain reaction temperature from the isocyanategroups they block, or are released again by a substitution reaction inthe presence of the crosslinking agent (2); and

(1.10) at least one neutralizing agent for the anionic stabilization inthe aqueous medium, which comprises or consists of organic and/orinorganic bases.

In the text below, the novel reactive polyurethane is referred to as the“polyurethane of the invention”.

The invention also provides the novel polyurethane dispersion whichcomprises at least one polyurethane of the invention in dispersion in anaqueous medium.

In the text below, the novel polyurethane dispersion is referred to asthe “polyurethane dispersion of the invention”.

The invention further provides the novel solvent-free coating material,especially basecoat and/or clearcoat or solid-color topcoat material,which comprises at least one polyurethane of the invention and/or onepolyurethane dispersion of the invention.

In the text below, the novel solvent-free coating material is referredto as the “coating material of the invention”.

The invention additionally provides a novel process for producingsingle-coat and multicoat coating systems, in which the coating materialof the invention is used.

In the text below, the novel process for producing single-coat andmulticoat systems is referred to as the “process of the invention”.

The invention provides, moreover, novel single-coat and multicoatsystems produced using the coating material of the invention and/or withthe aid of the process of the invention.

In the text below, the novel single-coat and multicoat systems arereferred to as the “coating systems of the invention”.

The invention provides not least novel primed or unprimed substrateswhich carry the coating systems of the invention and which are referredto below as “substrates of the invention”.

In the light of the prior art it was surprising and unforeseeable forthe skilled worker that the object on which the present invention isbased might be achieved with the aid of the polyurethane of theinvention or, respectively, the polyurethane dispersion of theinvention, especially since the polyurethane dispersions known from theprior art still always necessarily include a comparatively high solventfraction in order for their profile of properties to meet all of therequirements.

The polyurethane of the invention has a number-average molecular weightMn of from 800 to 14000 daltons, preferably from 1500 to 6000 daltons.It has a degree of branching of from 0.0 to 3.0 mol/kg, preferably from0.1 to 1.0 mol/kg. Its functionality, based on the blocked isocyanategroups, is from 2.0 to 6.0, preferably from 2.5 to 4.0 per mol.

The polyurethane of the invention is preparable from the startingproducts (1.1) to (1.10).

In accordance with the invention, at least one polyester is used asstarting product (1.1) and at least one polyether is used as startingproduct (1.2). The starting products (1.1) and (1.2) may each be usedindividually or as a mixture to prepare the polyurethane of theinvention. In accordance with the invention, the polyesters (1.1) are ofadvantage and are therefore used with preference.

The starting products (1.1) and (1.2) contain at least twoisocyanate-reactive functional groups. Examples of suitable suchfunctional groups are thio, amino, hydroxyl, or epoxide groups. Inaccordance with the invention, hydroxyl groups are advantageous and aretherefore used with preference.

The polyesters (1.1) and polyethers (1.2) have molecular masses of from400 to 2500 daltons, preferably from 800 to 1800 daltons, and a degreeof branching of from 0 to 3.5 mol/kg.

The polyesters (1.1) for use in accordance with the invention areobtainable by reacting polycarboxylic acids, polyols and, if desired,monocarboxylic acids.

Examples of suitable polycarboxylic acids are aromatic polycarboxylicacids such as terephthalic acid, isophthalic acid, phthalic acid,trimellitic acid or pyromellitic acid and also their ring-substitutedalkyl derivatives; cycloaliphatic polycarboxylic acids such astetrahydrophthalic acid, 1,2-cyclobutanedicarboxylic acid,1,3-cyclobutanedicarboxylic acid, 1,2-cyclopentanedicarboxylic acid,1,3-cyclopentanedicarboxylic acid, hexahydrophthalic acid,1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid,4-methylhexahydrophthalic acid or tricyclodecanedicarboxylic acid, whichmay be used both in their cis forms and in their trans forms and also asa mixture of both forms; or acyclic polycarboxylic acids such as malonicacid, succinic acid, glutaric acid, adipic acid, pimelic acid, subericacid, azelaic acid, sebacic acid, undecanedicarboxylic acid ordodecanedicarboxylic acid, maleic acid, fumaric acid, itaconic acid,citraconic acid or dimer fatty acids.

Also suitable in accordance with the invention are the esterifiablederivatives of the abovementioned polycarboxylic acids, such as, forexample, their monoesters or polyesters with aliphatic alcohols having 1to 4 carbon atoms or hydroxy alcohols having 1 to 4 carbon atoms.Furthermore, it is also possible to use the anhydrides of theabovementioned polycarboxylic acids, where they exist.

Examples of suitable polyols are diols such as ethylene glycol, 1,2- or1,3-propanediol, methylpropane-1,3 diol, ether oligomers of ethyleneglycol and propylene glycol such as diethylene glycol or dipropyleneglycol, 1,2-, 1,3- or 1,4-butanediol, 1,2-, 1,3-, 1,4- or 1,5pentanediol, 1,2-, 1,3-, 1,4-, 1,5- or 1,6-hexanediol, neopentylhydroxypivalate, neopentyl glycol, 1,2-, 1,3 or 1,4-cyclohexanediol,1,2-, 1,3- or 1,4-cyclohexanedimethanol, tricyclodecanedimethanol (TCD),trimethylpentanediol, ethylbutylpropanediol, octanediols, nonanediols,the positionally isomeric diethyloctanediols,2-butyl-2-ethylpropane-1,3-diol, 2-butyl-2-methylpropane-1,3-diol,2-phenyl-2-methylpropane-1,3-diol, 2-propyl-2-ethylpropane-1,3-diol,2-di-tertbutylpropane-1,3-diol, 2-butyl-2-propylpropane-1,3-diol,1-dihydroxymethylbicyclo[2.2.1]heptane, 2,2-diethylpropane-1,3-diol,2,2-dipropylpropane-1,3-diol, 2-cyclohexyl-2-methylpropane-1,3-diol,2,5-dimethylhexane-2,5-diol, 2,5-diethylhexane-2,5-diol,2-ethyl-5-methylhexane-2,5-diol, 2,4-dimethylpentane-2,4-diol,2,3-dimethylbutane-2,3-diol, 1,4-di(2′-hydroxypropyl)benzene,1,3-di(2′-hydroxypropyl)benzene or dimer diols from dimer fatty acids;or triols such as glycerol, trimethylolethane, trimethylolpropane,trishydroxyethyl isocyanurate or pentaerythritol.

The diols and the triols are employed in a molar ratio which gives thedesired degree of branching.

Examples of suitable monocarboxylic acids, employed if desired, are2-ethylhexanoic acid, 3,3,5-trimethylexanoic acid, pelargonic acid,fatty acids from coconut oil, fatty acids from natural oils, resinacids, benzoic acid, and p-tert-butylbenzoic acid.

The polyester (1.1) is prepared by the known methods of esterification,as described for example in DE-A-40 24 204, page 4 lines 50 to 65. Thereaction usually takes place at temperatures of between 180 and 280° C.,in the presence or absence of an appropriate esterification catalyst,such as lithium octoate, dibutyltin oxide, dibutyltin dilaurate orpara-toluenesulfonic acid, for example.

The polyester (1.1) is normally prepared in the presence of smallamounts of an appropriate solvent as entrainer. Examples of entrainersused are aromatic hydrocarbons, such as in particular xylene and(cyclo)aliphatic hydrocarbons, e.g., cyclohexane or methylcyclohexane.

Examples of suitable polyethers (1.2) for use in accordance with theinvention are adducts of polyols, especially those described in detailabove, and ethylene oxide or propylene oxide or mixtures of the two inthe form of random or block copolymers.

In accordance with the invention, further starting products usedcomprise at least one polyol (1.3) having a molecular mass of from 62 to400 daltons and a functionality of from 2 to 4 and/or at least onepolyamine (1.4) and/or at least one alkanolamine (1.5) for thepreparation of the polyurethane of the invention.

Examples of suitable polyols (1.3) are the polyols described in detailabove.

Examples of suitable polyamines (1.4) are, e.g., hydrazine,ethylenediamine, propylenediamine, methyldiaminopropane, higheralkanediamines, diethylenetriamine, dipropylenetriamine,m-xylylenediamine, p-xylylenediamine, 4,4′-diaminodicyclohexane,4,4′-diamino-3,3′-dimethylcyclohexane or isomeric octanediamines.

Examples of suitable alkanolamines (1.5) are, e.g. ethanolamine,methylethanolamine, diisopropylamine, diethanolamine,N-methyldiethanolamine, hydroxyethoxyethylamine, polyetheramine-ols,aminomethylpropanol, trishydroxymethylaminomethane or triethanolamine.

In accordance with the invention, a further starting product usedcomprises at least one compound (1.6) having at least one functionalgroup capable of forming anions and at least one, in particular at leasttwo, isocyanate-reactive functional group(s) for the preparation of thepolyurethane of the invention.

Examples of suitable functional groups capable of forming anions arecarboxylic acid, sulfonic acid and phosphonic acid groups, of which thecarboxylic acid groups are particularly advantageous and are thereforeused with preference in accordance with the invention.

Examples of suitable isocyanate-reactive functional groups are thosedescribed above, of which the hydroxyl groups are of advantage inaccordance with the invention and are therefore employed withpreference.

Examples of compounds (1.6) used with preference are dimethylolpropionicacid, hydroxypivalic acid, the reaction product of ethylenediamine andacrylic acid, the reaction product of a diol diester of maleic acid andsulfurous acid, or the alkali metal salts thereof.

In accordance with the invention, further starting products used toprepare the polyurethane of the invention comprise at least onepolyisocyanate (1.7) and/or at least one polyisocyanate adduct (1.8).

Suitable polyisocyanates (1.7) in principle are all of the customary andknown polyisocyanates used in the coatings field, which are alsoreferred to as paint polyisocyanates.

Examples of suitable polyisocyanates (1.7) are isophorone diisocyanate(i.e., 5-isocyanato-1-isocyanatomethyl-1,3,3-trimethylcyclohexane),5-isocyanato-1-(2-isocyanatoeth-1-yl)-1,3,3-trimethylcyclohexane,5-isocyanato-1-(3-isocyanatoprop-1-yl)-1,3,3-trimethylcyclohexane,5-isocyanato-(4-isocyanatobut-1-yl)-1,3,3-trimethylcyclohexane,1-isocyanato-2-(3-isocyanatoprop-1-yl)cyclohexane,1-isocyanato-2-(3-isocyanatoeth-1-yl)cyclohexane,1-isocyanato-2-(4-isocyanatobut-1-yl)cyclohexane,1,2-diisocyanatocyclobutane, 1,3-diisocyanatocyclobutane,1,2-diisocyanatocyclopentane, 1,3-diisocyanatocyclopentane,1,2-diisocyanatocyclohexane, 1,3-diisocyanatocyclohexane,1,4-diisocyanatocyclohexane, dicyclohexylmethane 2,4′-diisocyanate,dicyclohexylmethane 4,4′-diisocyanate, trimethylene diisocyanate,tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylenediisocyanate, ethylethylene diisocyanate, trimethylhexane diisocyanate,heptamethylene diisocyanate, or diisocyanates derived from dimer fattyacids, as sold under the commercial designation DDI 1410 by the companyHenkel and described in the patents WO 97/49745 and WO 97/49747,especially 2-heptyl-3,4-bis(9-isocyanatononyl)-1-pentylcyclohexane,1,2-, 1,4- or 1,3-bis(isocyanatomethyl)cyclohexane, 1,2-, 1,4- or1,3-bis(2-isocyanatoeth-1-yl)cyclohexane,1,3-bis(3-isocyanatoprop-1-yl)cyclohexane or 1,2-, 1,4- or1,3-bis(4-isocyanatobut-1-yl)cyclohexane, m-tetramethylxylylenediisocyanate (i.e., 1,3-bis(2-isocyanatoprop-2-yl)benzene), or tolylenediisocyanate.

Examples of suitable polyisocyanate adducts (1.8) areisocyanato-containing polyurethane prepolymers, which may be prepared byreacting polyols with an excess of polyisocyanates and which are ofpreferably low viscosity. It is also possible to use polyisocyanatescontaining isocyanurate, biuret, allophanate, iminooxadiazinedione,urethane, urea, carbodiimide and/or uretdione groups. Polyisocyanatescontaining urethane groups, for example, are obtained by reacting someof the isocyanate groups with polyols, such as trimethylolpropane andglycerol, for example. It is preferred to use the polyisocyanates (1.7)described in detail above.

Very particular preference is given to using mixtures of polyisocyanateadducts (1.8) based on hexamethylene diisocyanate and containinguretdione and/or isocyanurate groups and/or allophanate groups, asformed by catalytic oligomerization of hexamethylene diisocyanate usingappropriate catalysts. Moreover, the polyisocyanate constituent may alsoconsist of any desired mixtures of the free polyisocyanates (1.7)mentioned by way of example.

In accordance with the invention, at least one blocking agent (1.9) isused to prepare the polyurethane of the invention. As is known, theseblocking agents are eliminated again at a certain reaction temperaturefrom the isocyanate groups they block, or are released again by way of asubstitution reaction in the presence of the crosslinking agent (2)described below.

Examples of suitable blocking agents (1.9) are

i) phenols such as phenol, cresol, xylenol, nitrophenol, chlorophenol,ethylphenol, t-butylphenol, hydroxybenzoic acid, esters of this acid, or2,5-di-tert-butyl-4-hydroxytoluene;

ii) lactams, such as ε-caprolactam, δ-valerolactam, γ-butyrolactam orβ-propiolactam;

iii) active methylenic compounds, such as diethyl malonate, dimethylmalonate, ethyl or methyl acetoacetate, or acetylacetone;

iv) alcohols such as methanol, ethanol, n-propanol, isopropanol,n-butanol, isobutanol, t-butanol, n-amyl alcohol, t-amyl alcohol, laurylalcohol, ethylene glycol monomethyl ether, ethylene glycol monoethylether, ethylene glycol monobutyl ether, diethylene glycol monomethylether, diethylene glycol monoethyl ether, propylene glycol monomethylether, methoxymethanol, glycolic acid, glycolic esters, lactic acid orlactic esters;

v) mercaptans such as butyl mercaptan, hexyl mercaptan, t-butylmercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol,methylthiophenol or ethylthiophenol;

vi) acid amides such as acetoanilide, acetoanisidinamide, acrylamide,methacrylamide, acetamide, stearamide or benzamide;

vii) imides such as succinimide, phthalimide or maleimide;

viii) amines such as diphenylamine, phenylnaphthylamine, xylidine,N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine,dibutylamine or butylphenylamine;

ix) imidazoles such as imidazole or 2-ethylimidazole;

x) ureas such as urea, thiourea, ethyleneurea, ethylenethiourea or1,3-diphenylurea;

xi) carbamates such as phenyl N-phenylcarbamate or 2-oxazolidone;

xii) imines such as ethyleneimine;

xiii) oximes such as acetone oxime, formaldoxime, acetaldoxime,acetoxime, methyl ethyl ketoxime, diisobutyl ketoxime, diacetylmonoxime, benzophenone oxime or chlorohexanone oximes;

xiv) salts of sulfurous acid such as sodium bisulfite or potassiumbisulfite;

xv) hydroxamic esters such as benzyl methacrylohydroxamate (BMH) orallyl methacrylohydroxamate; or

xvi) substituted pyrazoles, ketoximes, imidazoles or triazoles; and also

xvii) mixtures of these blocking agents, especially dimethylpyrazole andtriazoles, malonic esters and acetoacetic esters or dimethylpyrazole andsuccinimide.

In accordance with the invention, neutralizing agents (1.10) are used toprepare the polyurethanes of the invention.

The neutralizing agents (1.10) comprise organic and/or inorganic,especially organic, bases, or consist thereof.

Examples of suitable inorganic bases are alkali metal hydroxides,ammonia or salts which release ammonia; examples of suitable organicbases are amines, preferably tertiary amines such as triethylamine,N,N-dimethylethanolamine, and triethanolamine.

Particularly advantageous polyurethanes of the invention result from thereaction of polyesters (1.1) which have been formed from cycloaliphaticand aliphatic polycarboxylic acids with cycloaliphatic or aliphaticdiisocyanates (1.7), triols (1.3) and ketoximes, dimethylpyrazole,acetoacetates and malonic esters, and/or mixtures thereof, as blockingagents

The nature and amount of the starting products described in detail aboveare selected so as to give a polyurethane of the invention having theabove-defined specification.

In accordance with the invention, the blocking agent (1.9) is used herein a molar ratio of from 0.9 to 1.3, based on the isocyanate groupswhich are not reactable or reacted with the other starting products, andthe neutralizing agent (1.10) is used in a molar ratio of from 0.5 to1.2, based on the functional groups of the compounds (1.6) that arecapable of forming anions.

Otherwise, the skilled worker is able to make the election on the basisof his or her general knowledge in the art, possibly with the assistanceof simple preliminary tests.

The polyurethanes (1) of the invention are prepared by conventionalprocesses. By way of example, reference may be made to the patentsEP-A-0 355 433, DE-A-35 45 618, DE-A-38 13 866, DE-A-32 10 051, DE-A-2624 442, DE-A-37 39 332, U.S. Pat. No. 4,719,132, EP-A-0 089 497, U.S.Pat. No. 4,558,090, U.S. Pat. No. 4,489,135, DE-A-36 28 124, EP-A-0 158099, DE-A-29 26 584, EP-A-0 195 931, DE-A-33 21 180 and DE-A-40 05 961.

Accordingly, the starting products—polyesters (1.1) and/or polyethers(1.2), polyols (1.3), polyamines (1.4) and/or alkanolamines (1.5),compounds (1.6), polyisocyanates (1.7) and/or polyisocyanate adducts(1.8)—are reacted in the presence or absence of a solvent, which is ofcomparatively high volatility, is soluble in water and is unable toreact with the isocyanates, and also in the presence, if desired, ofeffective amounts of catalysts, at temperatures of from 50 to 120° C.Examples of suitable solvents are lower ketones such as acetone, methylethyl ketone or methyl isobutyl ketone. Examples of suitable catalystsare tin salts. The result is a polyurethane prepolymer, branched ifdesired, containing terminal free isocyanate groups.

The prepolymer may also be synthesized in stages. The reaction ismonitored by determining the NCO equivalent weight and, if appropriate,measuring the viscosity of a defined measurement solution.

Subsequently, the remaining free isocyanate groups are reacted with theblocking agent (1.9) at temperatures from 50 to 120° C. Certain blockingagents (1.9) necessitate the use of catalysts, such as alkali metalphenoxide, for example, in the case of acetoacetate and malonic esters.The conversion is monitored by determining the NCO equivalent weight,and the reaction is normally carried out until the concentration of theisocyanate groups has fallen below the detection limit. The result is apolyurethane, branched if desired, containing a certain amount ofreactive capped isocyanate groups and functional groups, capable offorming anions, from the incorporated compounds (1.6). These functionalgroups of the polyurethane in the abovementioned process solvent arethen neutralized with a defined amount of a neutralizing agent (1.10),so giving the polyurethane of the invention.

The polyurethane of the invention is then dispersed in an aqueousmedium, so giving the polyurethane dispersion of the invention.

The aqueous medium substantially comprises, or consists of, water. Inthis context, the aqueous medium may contain minor amounts of theabove-described neutralizing agents (1.10), the crosslinking agents (2)and/or coatings additives (3) described above, and/or other dissolvedsolid, liquid or gaseous, organic and/or inorganic, low and/or highmolecular mass substances. In the context of the present invention, theterm “minor amount” means an amount which does not destroy the aqueouscharacter of the aqueous medium. Preferably, water alone is used.

The solvent and any excess of blocking agent (1.9) are removed from thepolyurethane dispersion of the invention down to below their detectionlimits by vacuum distillation at temperatures from 50 to 110° C. Thisgives a solvent-free polyurethane dispersion of the invention withanionic stabilization.

One variant of the above-described process for preparing thepolyurethane of the invention and the polyurethane dispersion process ofthe invention comprises allowing the polyisocyanates (1.7) and/orpolyisocyanate adducts (1.8) first to undergo partial initial reactionwith the blocking agent (1.9) and only then reacting them with the otherstarting products.

The coating materials of the invention comprise at least onecrosslinking agent (2) having functional groups which are able toundergo crosslinking reactions with the blocked isocyanate groups of thepolyurethanes of the invention at relatively high temperatures, inparticular temperatures above 80° C.

Another process variant comprises conducting the reaction of thepolyurethane prepolymer with the blocking agent until a comparativelylow NCO equivalent weight is reached and then reacting the remainingisocyanate groups with the polyols (1.3), polyamines (1.4) and/oralkanolamines (1.5) for the further synthesis of the molecule.

In the case of yet another process variant, this molecular synthesiswith polyamines (1.4) and/or alkanolamines (1.5) takes place only afterthe neutralization, or together with the neutralization, in the aqueousmedium.

Another particular process variant comprises allowing the polyurethaneprepolymer, still containing free isocyanate groups and cappedisocyanate groups, to react with water in the aqueous medium during theneutralization; in this case, part of the product formed from theisocyanate groups comprises amino groups, which react with otherisocyanate groups to give urea groups, a reaction accompanied by chainextension.

The polyurethane of the invention and the polyurethane dispersion of theinvention are used to prepare the coating materials of the invention,especially the clearcoat or topcoat materials of the invention.

The coating materials of the invention comprise at least onecrosslinking agent (2) having functional groups which are able toundergo crosslinking reactions with the blocked isocyanate groups of thepolyurethanes of the invention at relatively high temperatures, inparticular temperatures above 800C [sic].

Examples of suitable crosslinking agents (2) are polyols (2.1),polyamines (2.2) and/or alkanolamines (2.3), especially those which arenot markedly volatile at room temperature and are also water-soluble orare water-dilutable in conjunction with the polyurethane of theinvention.

Examples of suitable polyols (2.1) are the polyols described above,provided they meet the abovementioned conditions, especially ethyleneglycol, propylene glycol, ether oligomers of ethylene glycol andpropylene glycol, propane-1,3-diol, butane-1,4-diol, butane-1,3-diol,methylpropane-1,3-diol, pentane-1,5-diol, methylbutane-1,4-diol,neopentyl glycol, hexane-1,6-diol, glycerol, trimethylolethane,trimethylolpropane or trishydroxyethyl isocyanurate, especiallytrishydroxyethyl isocyanurate.

Examples of suitable polyamines (2.2) are ethylenediamine,propylenediamine, methyldiaminopropane, diethylenetriamine,dipropylenetriamine, m-xylylenediamine, p-xylylenediamine,4,4′-diaminodicyclohexane or 4,4′-diamino-3,3′-dimethylcyclohexane.

Examples of suitable alkanolamines (2.3) are ethanolamine,methylethanolamine, diisopropylamine, diethanolamine,N-methyldiethanolamine, hydroxyethoxyethylamine, polyetheramine-ols,aminomethylpropanol, trishydroxymethylaminomethane or triethanolamine.

Advantageously, the polyol (2.1), the polyamine (2.2) and/or thealkanolamine (2.3) is or are used in an amount such that the ratio of(i) equivalent weight of the polyurethane of the invention, based on theblocked isocyanate groups present therein, to (ii) equivalent weight ofthe crosslinking agent (2) is from 0.6 to 1.3.

The coating material of the invention may comprise customary coatingsadditives (3) in effective amounts. The nature and amount of theadditives (3) are guided in particular by the intended use of thecoating material of the invention. A critical factor is that theseadditives (3) should be nonvolatile under the processing and applicationconditions of the coating material of the invention, so that onlyorganic constituents which are volatile on thermal curing (baking), suchas the neutralizing agents (1.10), blocking agents (1.9), additives (3)or degradation products, are released.

Where the coating material of the invention is used as a basecoat orsolid-color topcoat material, it comprises color and/or effect pigments(3.1) in customary and known amounts. The pigments (3.1) may consist oforganic or inorganic compounds and may impart effect and/or color. Onthe basis of this large number of suitable pigments, therefore, thecoating material of the invention ensures a universal scope of use ofthe coating materials and permits the realization of a large number ofshades and optical effects.

As effect pigments (3.1) it is possible to use metal flake pigments suchas commercially customary aluminum bronzes, aluminum bronzes chromatedin accordance with DE-A-36 36 183, and commercially customary stainlesssteel bronzes, and also nonmetallic effect pigments, such as pearlescentpigments and interference pigments, for example. Use is made inparticular of those effect pigments (3.1) which are stable in aqueousmedia. Examples of suitable inorganic color pigments (3.1) are titaniumdioxide, iron oxides, Sicotrans yellow, and carbon black. Examples ofsuitable organic color pigments are indanthrene blue, Cromophthal red,Irgazine orange and Heliogen green.

The coating material of the invention may further comprise organic andinorganic fillers (3.1) in customary and known, effective amounts.Examples of suitable fillers are chalk, calcium sulfate, barium sulfate,silicates such as talc or kaolin, silicas, oxides such as aluminumhydroxide or magnesium hydroxide, nanoparticles, or organic fillers suchas textile fibers, cellulose fibers, polyethylene fibers or wood flour.

These additives (3.1) are omitted if the coating materials of theinvention are used as clearcoat materials.

Examples of suitable additives (3) which may be present in both theclearcoat materials and topcoat materials of the invention are

UV absorbers (3.2);

free-radical scavengers (3.3);

crosslinking catalysts (3.4);

slip additives (3.5);

polymerization inhibitors (3.6);

defoamers (3.7);

emulsifiers (3.8), especially nonionic emulsifiers such as alkoxylatedalkanols and polyols, phenols and alkylphenols, or anionic emulsifierssuch as alkali metal salts or ammonium salts of alkanecarboxylic acids,alkanesulfonic acids, and sulfo acids of alkoxylated alkanols andpolyols, phenols and alkylphenols;

wetting agents (3.9) such as siloxanes, fluorine compounds, carboxylicmonoesters, phosphoric esters, polyacrylic acids and their copolymers,or polyurethanes;

adhesion promoters (3.10);

leveling agents (3.11);

film-forming auxiliaries (3.11) such as cellulose derivatives;

flame retardants or

rheology control additives (3.12) such as those known from the patentsWO 94/22968, EP-A-0 276 501, EP-A-0 249 201 or WO 97/12945; crosslinkedpolymeric microparticles, as disclosed for example in EP-A-0 008 127;inorganic phyllosilicates such as aluminum magnesium silicates, sodiummagnesium phyllosilicates and sodium magnesium fluorine lithiumphyllosilicates of the montmorillonite type; silicas such as Aerosils;or synthetic polymers containing ionic and/or associative groups, suchas polyvinyl alcohol, poly(meth)acrylamide, poly(meth)acrylic acid,polyvinylpyrrolidone, styrene-maleic anhydride copolymers orethylene-maleic anhydride copolymers and their derivatives, orhydrophobically modified ethoxylated urethanes or polyacrylates.

Further examples of suitable additives (3) are described in the textbook“Lackadditive” [Additives for coatings] by Johan Bieleman, Wiley-VCH,Weinheim, New York, 1998.

Viewed in terms of its method, the preparation of the coatingcomposition of the invention has no special features but instead takesplace in a customary and known manner by mixing of its constituents incustomary and known mixing equipment such as dissolvers. In thiscontext, the crosslinking agent (2) may be added per se or in solutionin water to the polyurethane dispersion of the invention. Then theadditives (3) are added. Thereafter, the viscosity is adjusted withwater to the desired processing viscosity. Alternatively, the additives(3) may be added to the organic phase following the preparation of thepolyurethane of the invention, after which they are converted into thepolyurethane dispersion of the invention together with the polyurethaneof the invention. Alternatively, the crosslinking agent (2) may be mixedin organic phase with the polyurethane of the invention; the resultingorganic solution is then dispersed in an aqueous medium and the organicsolvent is stripped off or distilled off, under reduced pressure ifdesired.

For processing and application, the solids content of the coatingmaterials of the invention may be varied widely. In accordance with theinvention, however, it is of advantage if the coating materials of theinvention have a solids content of from 25 to 55% by weight, preferablyfrom 30 to 45% by weight.

The coating material of the invention may be applied by customaryapplication methods, such as spraying, knife coating, brushing, flowcoating, dipping or rolling, for example, to any desired, primed orunprimed substrates such as metal, wood, plastic, glass or paper,especially metal. In the case of plastics, the customary and knownwater-based primers may be employed. In the case of metals, it is commonto use primers produced from cathodic electrodeposition coatingmaterials and primer-surfacers.

The coating materials of the invention are outstandingly suitable forthe production of single-coat or multicoat coating systems, especiallyautomotive OEM finishes, industrial coatings, including coil coatingsand container coatings, and furniture coatings. In all end uses, theymay be used as basecoat materials and/or clearcoat materials orsolid-color topcoat materials. With particular advantage they are usedfor the OEM finishing of automobiles.

For the production of the single-coat and multicoat coating systems ofthe invention, the coating materials of the invention, following theirapplication, are cured thermally at relatively high temperatures. It isadvantageous in this case to employ temperatures of from 80° to 180°,preferably from 100 to 170, and in particular from 120 to 160° C. Theduration of curing may vary widely and depending on the coating materialof the invention may be from one minute up to several hours. For thethermal curing it is possible to employ the customary and knownequipment such as forced-air ovens or IR lamps.

The coating material of the invention is of outstanding suitability inparticular for the production of multicoat coating systems of theinvention by the process of the invention.

The process of the invention starts in step (I) from the application ofa basecoat material to the substrate surface or to the primer. Theresulting basecoat film is not cured but merely dried. In step (II) ofthe process, the clearcoat material is applied wet-on-wet, followed bycuring of the resulting basecoat/clearcoat film in step (III) of theprocess. In accordance with the invention, the basecoat material and/orthe clearcoat material comprise(s) a coating material of the invention.If the basecoat material or clearcoat material used is not a coatingmaterial of the invention, customary and known aqueous basecoatmaterials, or customary and known clearcoat materials, are used instead.

The result is continuous, substantially diffusion-impervious, hard,glossy, elastic, single-coat or multicoat coating systems of theinvention, without defects such as popping marks, streaks or cloudiness(haze), which are notable, furthermore, for particularly high chemicalresistance and weathering stability.

EXAMPLES Preparation Example 1 Preparation of the PolyurethaneDispersion of the Invention

A 4 l useful capacity, stainless steel reactor with a close-clearancestirrer, a reflux condenser, regulatable oil heating and temperaturemeasurement for the reaction mixture was charged with 1447 g of a 75%strength solution in methyl ethyl ketone of a saturated polyester (1.1)prepared from hexahydrophthalic anhydride, neopentyl glycol andhexane-1,6-diol and having an average molecular mass of 1085 daltons, annumber of 93.4 and an acid number of 10, 40.2 g of trimethylolpropane,227.8 g of dimethylolpropionic acid, 954.6 g of isophorone diisocyanateand 711.3 g of methyl ethyl ketone. The reaction mixture was carefullyheated to 82° C., thereby establishing reflux. The reaction mixture washeld at from 80 to 82° C. until the NCO equivalent weight, based on thesolution, reached 1350. It was then cooled to 50° C. and 200.1 g ofmethyl ethyl ketoxime were added. The reaction mixture was heated at 70°C. until the NCO equivalent weight, based on the solution, had risen tomore than 25000. Then the reaction mixture, in 3000 g of deionized waterwhich had been heated to 50° C., was mixed with 121 g ofN,N-dimethylethanolamine, after which the mixture was dispersed.

The resulting polyurethane dispersion was introduced into a reactorequipped with a condenser and receiver for a vacuum distillation, andwas heated to 60° C. From the start a reduced pressure of 75 mm wasapplied, after which distillation was carried out at 60° C. for twohours. After that time, the methyl ethyl ketone content was below 0.02%by weight.

The resulting solvent-free polyurethane dispersion was adjusted withdeionized water and a further quantity of N,N-dimethylethanolamine to asolids content of 40% by weight, and a pH of 7.8 was established. Thepolyurethane present in the dispersion had a number-average molecularweight of 2508 daltons, a degree of branching of 0.12 mol/kg, an acidnumber of 43, and an equivalent weight, based on the blocked isocyanategroups, of 1090.

Preparation Example 2 Preparation of a Clearcoat Material of theInvention

83.25 parts by weight of the polyurethane dispersion from preparationexample 1 were mixed with 2.65 parts by weight of trishydroxyethylisocyanurate, 2 parts by weight of a 10% strength solution of anethoxylated nonylphenol, 2 parts by weight of a 3% strength solution ofa polyacrylic acid, and 10.1 parts by weight of deionized water and themixture was homogenized by means of intensive stirring. The result wasan aqueous, solvent-free clearcoat material having a solids content, ora nonvolatile constituents content, of 36% by weight.

Example Production of a Multicoat System of the Invention

A customary and known aqueous silver metallic basecoat material wasapplied by pneumatic spraying to steel plates coated with a system whichis customary for automotive finishing, comprising an electrodepositioncoating material with a film thickness of 21 μm and an aqueousprimer-surfacer with a film thickness of 35 μm, and the basecoat filmwas predried at 80° C. for 10 minutes to give a film thickness of 16 μm.The aqueous clearcoat material from preparation example 2 was thenapplied by pneumatic spraying and predried at 60° C. for 5 minutes. Thepredried coating films were then cured in a baking oven at a forced-airtemperature of 155° C. for 20 minutes. The dry film thickness of theclearcoat was 42 μm.

This gave a smooth, glossy multicoat system which had no defects such aspopping marks, streaks or cloudiness (haze), exhibited a high metalliceffect, and was of pronounced resistance to chemicals, as underscored bycustomary and known test procedures such as those, for instance, whichare well known to the skilled worker.

In the case of the MB gradient oven test, the test panels of example 1were exposed under defined conditions to damage by sulfuric acid. Forthis purpose, dilute sulfuric acid, hydrochloric acid and sodiumhydroxide solution were applied by pipette (25 μl per drop) at adistance of one segment width in each case (adjustment of the gradientto 30-74° C. [1° C. per heating segment]). Following storage understandard climatic conditions (23° C.) for 72 hours, the test panels wereexposed for 30 minutes in a gradient oven (e.g. type 2615 fromBYK-Gardner). The temperatures at which the first visible changesoccurred were determined. In all cases, the temperatures were above 40°C.

What is claimed is:
 1. A reactive polyurethane having a number averagemolecular weight Mn of from 800 to 14000 daltons, a degree of branchingof from 0.0 to 3.0 mol/kg, and an isocyanate functionality from 2.0 to6.0 per mole, comprising the reaction product of: at least one polyesterthat has at least two isocyanate-reactive functional groups, a molecularmass of from 400 to 2500 daltons, and a degree of branching of from 0 to3.5 mol/kg; at least one of at least one polyol having a molecular massof from 62 to 400 daltons and a functionality of from 2 to 4, at eastone polyamine, and at least one alkanolamine, wherein at least one ofthe polyamine and the alkanolamine is present in the reaction product;at least one compound comprising at least one functional group capableof forming anions and at least one isocyanate-reactive functional group;at least one of at least one polyisocyanate and at least onepolyisocyanate adduct; at least one blocking agent for the isocyanategroups, wherein the blocking agent is eliminated at a sufficientreaction temperature from the isocyanate groups that are blocked by theblocking agent, or the blocking agent is released by a substitutionreaction in the presence of a crosslinking agent; and at least oneneutralizing agent for anionic stabilization in an aqueous mediumcomprising at least one of an organic base and an inorganic base;wherein the reaction product does not contain a polyether.
 2. Thereactive polyurethane as claimed in claim 1, wherein the number averagemolecular weight Mn is from 1500 to 6000 daltons, the degree ofbranching is from. 0.1 to 1.0 mol/kg and the functionality is from 2.5to 4.0 per mol., the isocyanate-reactive functional groups comprise OHgroups, the polyesters have a molecular mass of from 800 to 1800daltons, the functional groups that are capable of forming anions are atleast one of a carboxylic acid group, a phosphonic acid group, and asulfonic acid group, and the neutralizing agent comprises an organicbase.
 3. The reactive polyurethane as claimed in claim 1, wherein theblocking agent is used in a molar ratio of from 0.9 to 1.3, based on theisocyanate groups that are not reactable or reacted with the polyesters,the polyols, the polyamines, the alkanolamines, the compound comprisingat least one functional group capable of forming anions and at least oneisocyanate-reactive functional group, the polyisocyanates, and thepolyisocyanate adducts, and the neutralizing agent is used in a molarratio of from 0.5 to 1.2, based on the functional groups of thecompounds that are capable of forming anions.
 4. A polyurethanedispersion comprising at least one reactive polyurethane of claim 1 in adispersion in an aqueous medium.
 5. A method comprising preparing asolvent-free coating material, wherein the solvent-free coating materialcomprises the reactive polyurethane of claim
 1. 6. A solvent-freecoating material comprising at least one reactive polyurethane ofclaim
 1. 7. The solvent-free coating material of claim 6 furthercomprising a crosslinking agent that is at least one of at least onepolyol, at least one polyamine, and at least one alkanolamine.
 8. Thesolvent-free coating material of claim 7, wherein at least one of thepolyol, the polyamine, and the alkanolamine are not markedly volatile atroom temperature and are also water-soluble or water-dilutable inconjunction with the reactive polyurethane.
 9. The solvent-free coatingmaterial of claim 7, wherein at least one of the polyol, the polyamine,and the alkanolamine are used in an amount such that a ratio of (i)equivalent weight of the polyurethane, based on blocked isocyanategroups present therein, to (ii) equivalent weight of crosslinking agentis from 0.6 to 1.3.
 10. The solvent-free coating material of claim 6further comprising at least one coatings additive in an effectiveamount.
 11. A method comprising applying the solvent-free coatingmaterial of claim 6 to a substrate to form an at least one coat coatingsystem.
 12. A process for producing an at least one coat coating systemcomprising applying at least one solvent-free coating material of claim6 to a primed or unprimed substrate, and curing.
 13. A process forproducing a multicoat coating system on a primed or unprimed substratecomprising (I) applying a basecoat material to the primed or unprimedsubstrate, (II) applying a clearcoat material wet-on-wet to thebasecoat, and (III) curing the basecoat and clearcoat, wherein at leastone of the basecoat material and the clearcoat material comprise thesolvent-free coating material of claim
 6. 14. An at least one coatcoating system comprising the solvent-free coating material of claim 6.15. A substrate comprising the at least one coat coating system of claim14.
 16. A method comprising preparing a solvent-free coating material,wherein the solvent-free coating material comprises the polyurethanedispersion of claim
 4. 17. A solvent-free coating material comprising atleast one polyurethane dispersion of claim
 4. 18. The solvent-freecoating material of claim 17 further comprising a crosslinking agentthat is at least one of at least one polyol, at least one polyamine, andat least one alkanolamine.
 19. The solvent-free coating material ofclaim 18, wherein at least one of the polyol, the polyamine, and thealkanolamine are not markedly volatile at room temperature and are alsowater-soluble or water-dilutable in conjunction with the reactivepolyurethane.
 20. The solvent-free coating material of claim 18, whereinat least one of the polyol, the polyamine, and the alkanolamine are usedin an amount such that a ratio of (i) equivalent weight of thepolyurethane, based on blocked isocyanate groups present therein, to(ii) equivalent weight of crosslinking agent is from 0.6 to 1.3.
 21. Thesolvent-free coating material of claim 17 further comprising at leastone coatings additive in an effective amount.
 22. A method comprisingapplying the solvent-free coating material of claim 17 to a substrate toform an at least one coat coating system.
 23. A process for producing anat least one coat coating system comprising applying at least onesolvent-free coating material of claim 17 to a primed or unprimedsubstrate, and curing.
 24. A process for producing a multicoat coatingsystem on a primed or unprimed substrate comprising (I) applying abasecoat material to the primed or unprimed substrate, (II) applying aclearcoat material wet-on-wet to the basecoat, and (III) curing thebasecoat and clearcoat, wherein at least one of the basecoat materialand the clearcoat material comprise the solvent-free coating material ofclaim
 17. 25. An at least one coat coating system comprising thesolvent-free coating material of claim
 17. 26. A substrate comprisingthe at least one coat coating system of claim 25.